The long term objective of this project is to further our knowledge of the many cell surface molecules on developing retinal axons and on their specific target tissue, the tectal regions of the brain. The retinotectal map is highly ordered and appears to be formed under the guidance of, among other influences, specific directional cues. Two dimensional gel analyses of cell surface and extracellular proteins from these tissues reveal the existence of a large number of proteins and protein families about which little is known. Some of these proteins are expressed on subsets of retinotectal fibers in previously undescribed patterns, as detected by monoclonal antibodies generated by us in a preliminary study. The strategy for generating monoclonal antibodies, based on knowledge of cell receptors that mediate specific cell/cell interactions in other systems, assumes that: molecules involved in specific axonal-axonal, axonal-tectal and other interactions of greatest importance in establishing pathways or directional cues are likely to include proteins which are very scarce and which are expressed on the cell surface or in the extracellular matrix. Cell surface and matrix proteins were therefore isolated from the visual system of chick embryos and were further fractionated prior to their use as immunogens. Immunization protocols were selected to help break tolerance and encourage response to rare antigens. Antibodies staining subsets of cells or axons in interesting patterns were selected for study. This proposal is to further characterize the reactivity of a panel of anti-retinotectal antibodies and to analyze the proteins with which they react.